The present invention relates to a device for imaging prints and suitable in particular for providing a representation of a fingerprint, a palm print or a ridge pattern of human tissues for instance for identification purposes.
Numerous devices already exist that are capable of forming a recordable image of the pattern of ridges on the end phalange of a finger. However, they enable the image to be recorded by a sensor only by using an external light source (U.S. Pat. Nos. 5,448,649, 4,340,300, 4,336,998). U.S. Pat. No. 4,336,998 describes a device comprising a transparent electrically insulating substrate, a thin transparent electrode, and a sensing layer for receiving finger pressure. The sensing layer is made of a thermoplastic material, such as polystyrene. When a finger is pressed on the sensing layer, its ridges are printed therein and remain temporarily after the finger has been removed. Thereafter, the relief of the imprint is reinforced by the action of an electric field for depositing electric charges and by heating the material to soften it prior to taking the image by means of an external light source and an optical sensor.
That device has numerous shortcomings. It is not very accurate since details do not show up because the material of the sensing layer is insufficiently flexible. It takes a long time to take a print. An electrical source delivering a high voltage is required. Finally, the device cannot distinguish between a human finger and a molding of a finger.